/**
* Select an item in the dropdown list by its numeric index in the list. This
* function does NOT cause the select event to fire. The list must expanded
* for this function to work, otherwise use #setValue.
*
* @param index the index of the item to select
*/
public void select(int index) {}

You most likely want to be using setValue. select should only be used when the list is expanded. I changed the code so that the null pointer will not be thrown.